Week 13 Earth Lab

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THE ASSIGNMENT

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[Assignment 1] - "Metamorphic Rocks"

Complete the attached PDF called - Metamorphic_Rocks.pdf (1.18 MB)

[Assignment 2] - "The Rock Cycle"

Complete the attached PDF called - The_Rock_Cycle.pdf (851 KB)

[Assignment 3] - "Week 13 Forum" - Answer the questions below for the discussion.

Of all the rocks we have studied, which one do you find the most interesting? Using the rock cycle, what type of rock could it have possibly been before what it is today? Using the rock cycle, what type of rock could it be next? - "300 word min"

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END OF ASSIGNMENT - The assignment should be submitted as follows or will request refund.

1. Assignment_1.docx or Assignment_1.pdf = "Metamorphic Rocks" - [REQUIRED]

2. Assignment_2.docx or Assignment_2.pdf = "The Rock Cycle" - [REQUIRED]

3. Assignment_3.docx or Assignment_3.pdf = "Week 13 Forum" - [REQUIRED]

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THANK YOU FOR YOUR HELP!

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Metamorphic Rocks For this lab, you will be making observations and interpretations about metamorphic rocks. I recommend that you print the data table provided and fill it in as you analyze each sample. Then, use your table to answer the questions at the end of the lab. Also answer these questions on our online class site so that you can get credit for the laboratory exercise. Metamorphism Metamorphic rocks form when pre-existing rocks are subjected to temperatures and/or pressures that are different from the environment in which they form. For example metamorphism can be caused by burial of rock, folding and thrusting of rock over other rock, heat from a pluton, or pressure from subduction. During metamorphism, rocks may undergo mineralogical and textural changes. During metamorphism, the rock does not melt. Instead it is a solid state recrystallization. Metamorphic Grade Metamorphic grade is the intensity of metamorphism to which the rock was subjected. In other words, it is a description of how much heat and pressure a rock has experienced in order to be changed to its current metamorphic state. Metamorphic grade is described as being low grade, medium grade, or high grade. During low-grade metamorphism, rock is exposed to relatively low temperatures and pressures (300-400°C; less than 3-4 kilobars). During medium-grade metamorphism, rock is exposed to intermediate temperatures and pressures (400-600°C; 4-12 kilobars). During high-grade metamorphism, rock is exposed to high temperatures and pressures (600-800°C; 12-15 kilobars). It is by studying the mineralogy and textures of metamorphic rocks that we are able to determine the degree or grade of metamorphism. Mineralogical Changes Each mineral is stable within a specific range of temperatures and pressures. When not at these temperatures or pressures, minerals can become unstable and react with each other to form new minerals. Therefore, we can analyze the suite of minerals in the rock and figure out what temperatures and pressures would be possible for each of those minerals to be present in the rock, thus determining the metamorphic grade. Textural Changes Textural refers to the size, shape, and orientation of grains in a rock. During metamorphism, heat and pressure can change the textures of rocks. Consider the sizes of minerals. Minerals may recrystallize to form larger crystals of the same minerals. For example, the calcite in fossiliferous limestone will recrystallize into large, interlocking crystals of calcite, forming marble, while the fossils, shells, and mud in the matrix are destroyed. Therefore, a rock with larger crystals of calcite would be formed. Some textural changes from metamorphism are a result of pressure being stronger in one direction than another, resulting in deformation, or change in shape. During deformation, it is common for platy minerals (like micas) to align perpendicular to the direction of compression, creating what is called foliation. Foliation is a texture that results from the parallelism of platy and flattened minerals in a metamorphic rock. Foliated rocks often have flat surfaces, especially in the minerals are too small to be visible. If foliation is present, you know you are dealing with low to medium metamorphism, where pressure was influential. Mica minerals do not withstand high temperatures. At high temperatures, micas will react with minerals around them to form feldspars and other minerals. If a metamorphic rock has bands of dark and light layers, it is considered compositionally layered, and is a sign of high grade metamorphism. If a metamorphic rock does not have layering or foliation, and instead has random, intergrown crystals, it is referred to as nonfoliated. This is usually a sign that pressure was not involved in the metamorphism. Protolith The protolith (proto=early, lith=rock), is the type of rock it used to be before the heat and pressure were added, transforming the rock into the metamorphic rock it is now. This is also often referred to as the parent rock. Since metamorphism can happen to any rock, even a metamorphic rock can be a protolith for another metamorphic rock. However, for the purposes of this class, we will go back all the way until the protolith was either a sedimentary or igneous rock. For example, when shale (a fissile, sedimentary mudstone) is metamorphosed, it first becomes slate, but upon application of more heat and pressure, the slate will change to phyllite, then schist, and finally gneiss. Therefore, the protolith for slate, phyllite, schist, and gneiss is shale. Gneiss actually has two protoliths, as seen in figure 1 below. This figure also shows the protoliths and other characteristics of common metamorphic rocks, which you will use to analyze metamorphic rocks. Figure 1. Common Metamorphic Rocks Major Additional Texture Minerals/Material Observations Micas – muscovite, Dull appearance, similar Foliated biotite, etc. to that of a chalkboard Has a sheen to it; Micas – muscovite, Foliated sometimes has wavy, biotite, etc. wrinkled surfaces Micas – muscovite, Foliated Often glittery appearance biotite, etc. Feldspars, quartz, Minerals are separated Layered hornblende into light and dark layers Nonfoliated Calcite Fizzes in acid Nonfoliated Quartz Nonfoliated Plant material (no minerals) Sometimes has a sugary texture; sometimes shows conchoidal fracture Black, low density, semimetallic luster Nonfoliated Graphite Writes on paper Nonfoliated Serpentine Waxy appearance, slippery feel Protolith Rock Name Shale Slate Shale Phyllite Shale Schist Shale or granite Gneiss Limestone Marble Sandstone Quartzite Bituminous coal Bituminous coal Basalt Anthracite Graphite Serpentinite Figure 2. Data table for observations of metamorphic rocks. Sample Texture Major Minerals/Material # 1 2 3 4 5 6 7 8 9 Additional Observations Protolith Rock Name Observe each of the images of samples of metamorphic rocks in Figure 3. Record your observations for appropriate textures and composition in the data table provided in Figure 2 (Hint: use information from Figure 1 to help you with ideas). Compare your data to the information in Figure 1 to help you classify each of the metamorphic rocks in this lab. Figure 4. Samples of Metamorphic Rocks (for scale, assume that each sample is actual size). Sample #1 Full View Sample #1 Close Up Sample #2 Full View (as well as a wavy, wrinkled surface.) Sample #2 Close Up (Notice that this has a sheen to it) Sample #3 Full View (If you were to pick it up, you would notice that this has very low density.) Sample #3 Close Up Sample #4 Full View Sample #4 Close Up (Notice: fizzes in HCl.) Sample #5 Full View Sample #5 Close Up Sample #6 Full View Sample #6 Close Up Sample #7 Full View Sample #7 Close Up Sample #8 Full View Sample #8 Close Up (This has a slippery feel to it.) Sample #9 Full View (Notice: this sample writes on paper.) Sample #9 Close Up Sample #10 Full View Sample #10 Close Up Answer the questions below. Use your completed data table (Figure 2) to answer these questions. You could skip these, and use your completed data table to answer the same questions online. 1. Sample #1: What is the texture of this rock? A. Foliated B. Layered C. Nonfoliated 2. Sample #1: What major mineral(s)/material makes up this rock? A. Micas (muscovite, biotite, etc.) B. Feldspar, quartz, and hornblende C. Calcite D. Quartz E. Plant material (no minerals) F. Graphite G. Serpentine 3. Sample #1: Which of the following is and additional observation that best describe this rock? A. Dull appearance, similar to that of a chalkboard B. Has a sheen to it; has wavy, wrinkled surfaces C. Glittery appearance D. Minerals are separated into light and dark layers E. Fizzes in acid F. Has conchoidal fracture G. Black, low density, semi-metallic luster H. Writes on paper I. Waxy appearance, slippery feel. 4. Sample #1: What is the protolith for this rock? A. Shale B. Shale or granite C. Limestone D. Sandstone E. Bituminous Coal F. Basalt 5. Sample #1: What is the name of this rock? A. Slate B. Phyllite C. Schist D. Gneiss E. Marble F. Quartzite G. Anthracite H. Graphite I. Serpentinite 6. Sample #2: What is the texture of this rock? A. Foliated B. Layered C. Nonfoliated 7. Sample #2: What major mineral(s)/material makes up this rock? A. Micas (muscovite, biotite, etc.) B. Feldspar, quartz, and hornblende C. Calcite D. Quartz E. Plant material (no minerals) F. Graphite G. Serpentine 8. Sample #2: Which of the following is and additional observation that best describe this rock? A. B. C. D. E. F. G. H. I. Dull appearance, similar to that of a chalkboard Has a sheen to it; has wavy, wrinkled surfaces Glittery appearance Minerals are separated into light and dark layers Fizzes in acid Has conchoidal fracture Black, low density, semi-metallic luster Writes on paper Waxy appearance, slippery feel. 9. Sample #2: What is the protolith for this rock? A. Shale B. Shale or granite C. Limestone D. Sandstone E. Bituminous Coal F. Basalt 10. Sample #2: What is the name of this rock? A. Slate B. Phyllite C. Schist D. Gneiss E. Marble F. Quartzite G. Anthracite H. Graphite I. Serpentinite 11. Sample #3: What is the texture of this rock? A. Foliated B. Layered C. Nonfoliated 12. Sample #3: What major mineral(s)/material makes up this rock? A. Micas (muscovite, biotite, etc.) B. Feldspar, quartz, and hornblende C. Calcite D. Quartz E. Plant material (no minerals) F. Graphite G. Serpentine 13. Sample #3: Which of the following is and additional observation that best describe this rock? A. Dull appearance, similar to that of a chalkboard B. Has a sheen to it; has wavy, wrinkled surfaces C. D. E. F. G. H. I. Glittery appearance Minerals are separated into light and dark layers Fizzes in acid Has conchoidal fracture Black, low density, semi-metallic luster Writes on paper Waxy appearance, slippery feel. 14. Sample #3: What is the protolith for this rock? A. Shale B. Shale or granite C. Limestone D. Sandstone E. Bituminous Coal F. Basalt 15. Sample #3: What is the name of this rock? A. Slate B. Phyllite C. Schist D. Gneiss E. Marble F. Quartzite G. Anthracite H. Graphite I. Serpentinite 16. Sample #4: What is the texture of this rock? A. Foliated B. Layered C. Nonfoliated 17. Sample #4: What major mineral(s)/material makes up this rock? A. Micas (muscovite, biotite, etc.) B. Feldspar, quartz, and hornblende C. Calcite D. Quartz E. Plant material (no minerals) F. Graphite G. Serpentine 18. Sample #4: Which of the following is and additional observation that best describe this rock? A. Dull appearance, similar to that of a chalkboard B. Has a sheen to it; has wavy, wrinkled surfaces C. Glittery appearance D. Minerals are separated into light and dark layers E. F. G. H. I. Fizzes in acid Has conchoidal fracture Black, low density, semi-metallic luster Writes on paper Waxy appearance, slippery feel. 19. Sample #4: What is the protolith for this rock? A. Shale B. Shale or granite C. Limestone D. Sandstone E. Bituminous Coal F. Basalt 20.Sample #4: What is the name of this rock? A. Slate B. Phyllite C. Schist D. Gneiss E. Marble F. Quartzite G. Anthracite H. Graphite I. Serpentinite 21. Sample #5: What is the texture of this rock? A. Foliated B. Layered C. Nonfoliated 22. Sample #5: What major mineral(s)/material makes up this rock? A. Micas (muscovite, biotite, etc.) B. Feldspar, quartz, and hornblende C. Calcite D. Quartz E. Plant material (no minerals) F. Graphite G. Serpentine 23. Sample #5: Which of the following is and additional observation that best describe this rock? A. Dull appearance, similar to that of a chalkboard B. Has a sheen to it; has wavy, wrinkled surfaces C. Glittery appearance D. Minerals are separated into light and dark layers E. Fizzes in acid F. Has conchoidal fracture G. Black, low density, semi-metallic luster H. Writes on paper I. Waxy appearance, slippery feel. 24. Sample #5: What is the protolith for this rock? A. Shale B. Shale or granite C. Limestone D. Sandstone E. Bituminous Coal F. Basalt 25. Sample #5: What is the name of this rock? A. Slate B. Phyllite C. Schist D. Gneiss E. Marble F. Quartzite G. Anthracite H. Graphite I. Serpentinite 26. Sample #6: What is the texture of this rock? A. Foliated B. Layered C. Nonfoliated 27. Sample #6: What major mineral(s)/material makes up this rock? A. Micas (muscovite, biotite, etc.) B. Feldspar, quartz, and hornblende C. Calcite D. Quartz E. Plant material (no minerals) F. Graphite G. Serpentine 28. Sample #6: Which of the following is and additional observation that best describe this rock? A. Dull appearance, similar to that of a chalkboard B. Has a sheen to it; has wavy, wrinkled surfaces C. Glittery appearance D. Minerals are separated into light and dark layers E. Fizzes in acid F. Has conchoidal fracture G. Black, low density, semi-metallic luster H. Writes on paper I. Waxy appearance, slippery feel. 29. Sample #6: What is the protolith for this rock? A. Shale B. Shale or granite C. Limestone D. Sandstone E. Bituminous Coal F. Basalt 30. Sample #6: What is the name of this rock? A. Slate B. Phyllite C. Schist D. Gneiss E. Marble F. Quartzite G. Anthracite H. Graphite I. Serpentinite 31. Sample #7: What is the texture of this rock? A. Foliated B. Layered C. Nonfoliated 32. Sample #7: What major mineral(s)/material makes up this rock? A. Micas (muscovite, biotite, etc.) B. Feldspar, quartz, and hornblende C. Calcite D. Quartz E. Plant material (no minerals) F. Graphite G. Serpentine 33. Sample #7: Which of the following is and additional observation that best describe this rock? A. Dull appearance, similar to that of a chalkboard B. Has a sheen to it; has wavy, wrinkled surfaces C. Glittery appearance D. Minerals are separated into light and dark layers E. Fizzes in acid F. Has conchoidal fracture G. Black, low density, semi-metallic luster H. Writes on paper I. Waxy appearance, slippery feel. 34. Sample #7: What is the protolith for this rock? A. Shale B. Shale or granite C. Limestone D. Sandstone E. Bituminous Coal F. Basalt 35. Sample #7: What is the name of this rock? A. Slate B. Phyllite C. Schist D. Gneiss E. Marble F. Quartzite G. Anthracite H. Graphite I. Serpentinite 36. Sample #8: What is the texture of this rock? A. Foliated B. Layered C. Nonfoliated 37. Sample #8: What major mineral(s)/material makes up this rock? A. Micas (muscovite, biotite, etc.) B. Feldspar, quartz, and hornblende C. Calcite D. Quartz E. Plant material (no minerals) F. Graphite G. Serpentine 38. Sample #8: Which of the following is and additional observation that best describe this rock? A. Dull appearance, similar to that of a chalkboard B. Has a sheen to it; has wavy, wrinkled surfaces C. Glittery appearance D. Minerals are separated into light and dark layers E. Fizzes in acid F. Has conchoidal fracture G. Black, low density, semi-metallic luster H. Writes on paper I. Waxy appearance, slippery feel. 39. Sample #8: What is the protolith for this rock? A. Shale B. C. D. E. F. Shale or granite Limestone Sandstone Bituminous Coal Basalt 40. Sample #8: What is the name of this rock? A. Slate B. Phyllite C. Schist D. Gneiss E. Marble F. Quartzite G. Anthracite H. Graphite I. Serpentinite 41. Sample #9: What is the texture of this rock? A. Foliated B. Layered C. Nonfoliated 42. Sample #9: What major mineral(s)/material makes up this rock? A. Micas (muscovite, biotite, etc.) B. Feldspar, quartz, and hornblende C. Calcite D. Quartz E. Plant material (no minerals) F. Graphite G. Serpentine 43. Sample #9: Which of the following is and additional observation that best describe this rock? A. Dull appearance, similar to that of a chalkboard B. Has a sheen to it; has wavy, wrinkled surfaces C. Glittery appearance D. Minerals are separated into light and dark layers E. Fizzes in acid F. Has conchoidal fracture G. Black, low density, semi-metallic luster H. Writes on paper I. Waxy appearance, slippery feel. 44. Sample #9: What is the protolith for this rock? A. Shale B. Shale or granite C. Limestone D. Sandstone E. Bituminous Coal F. Basalt 45. Sample #9: What is the name of this rock? A. Slate B. Phyllite C. Schist D. Gneiss E. Marble F. Quartzite G. Anthracite H. Graphite I. Serpentinite 46. Sample #10: What is the texture of this rock? A. Foliated B. Layered C. Nonfoliated 47. Sample #10: What major mineral(s)/material makes up this rock? A. Micas (muscovite, biotite, etc.) B. Feldspar, quartz, and hornblende C. Calcite D. Quartz E. Plant material (no minerals) F. Graphite G. Serpentine 48. Sample #10: Which of the following is and additional observation that best describe this rock? A. Dull appearance, similar to that of a chalkboard B. Has a sheen to it; has wavy, wrinkled surfaces C. Glittery appearance D. Minerals are separated into light and dark layers E. Fizzes in acid F. Has conchoidal fracture G. Black, low density, semi-metallic luster H. Writes on paper I. Waxy appearance, slippery feel. 49. Sample #10: What is the protolith for this rock? A. Shale B. Shale or granite C. Limestone D. Sandstone E. Bituminous Coal F. Basalt 50. Sample #10: What is the name of this rock? A. Slate B. Phyllite C. Schist D. Gneiss E. Marble F. Quartzite G. Anthracite H. Graphite I. Serpentinite The Rock Cycle For this lab, you will learn about and use the rock cycle. I recommend that you print the lab, record your answers, and then use those to input your answers into our online class site so that you can then get credit for the laboratory exercise. The rock cycle is the repeating events that gradually and continuously change rocks from one type to another. It is often displayed in diagrams that help to visualize this cycle, such as Figure 1 below. As an example, we will follow one possible cycle of the rock cycle, although there are many different paths that nature can take on the rock cycle. When magma either rises towards or reaches the surface, it cools and solidifies, undergoing crystallization to become igneous rock. Once they are at the surface, igneous rocks are slowly broken down by weathering, forming sediment. This sediment can be eroded and deposited. As sediment accumulates in layers, lithification begins, as it compacts and cements together, making a sedimentary rock. Over time, sedimentary rocks are buried under other sediments or are caught in movements of the crust that expose them to high temperatures and pressures, such as subduction. The heat and pressure causes them to change to metamorphic rock. When metamorphic rock is subjected to still higher temperatures, it can melt, forming magma. Therefore, we have completed one cycle, but the cycle keeps going. Rock does not need to take this same path, as there are alternative paths, depending on what is going on in nature in that area. Figure 1. The rock cycle Igneous Rock Key Crystallization Magma Sediment Weathering Metamorphosing Lithification Melting Metamorphic Rock Sedimentary Rock Part 1: Practice Using the Rock Cycle Using the rock cycle in Figure 1, fill in the missing information in order to change one given rock type to another. Ignore the numbers in parenthesis, as these will just be used to fill in your answers online. Magma (1)____________________________ into igneous rock. The igneous rock (2)____________________________ into sediment. The sediment (3)____________________________ to make sedimentary rock. The sedimentary rock becomes metamorphic rock due to (4)____________________________. The metamorphic rock melts, becoming (5)____________________________. Igneous rock (6)____________________________ to become metamorphic rock. The metamorphic rock (7)______________________ to become magma. The magma crystallizes to make (8)____________________________. Metamorphic rock (9)____________________________ into sediment. The sediment (10)____________________________ to make sedimentary rock. The sedimentary rock (11)____________________________ back into sediment. Igneous rock (12)____________________________ into sediment. Sediment compacts and cements to make (13)____________________________. Sedimentary rock metamorphoses into (14)____________________________, which is then weathered to make (15)____________________________. Igneous rock metamorphoses into (16)____________________________, which then (17)____________________________ to become magma. The magma crystallizes into (18)____________________________. This material then weathers into (19)____________________________, which then (20)____________________________ to make sedimentary rock. The repeating events that gradually and continuously changes rocks from one type to another is called the (21)____________________________ Part 2: Characterizing Processes and Rock Properties Indicate what rock group is characterized by each of the listed processes or rock properties in Figure 2. Figure 2. Characterizing processes and rock properties. Process or Property Igneous Sedimentary Lithification of sediment Intense heating (but no melting) Crystals precipitate from water Crystallization from magma Crystallization from lava Compaction of Sediment Cementation of sediment Folding, causing recrystallization Foliated Fossils present Melting of rock Metamorphic Part 3: Rock Cycle Predictions For each of the samples in Figure 3, and using the rock cycle diagram in Figure 1, determine where this rock would fall on the rock cycle. In other words, classify the rock as either igneous, sedimentary, or metamorphic (there are three of each category). Then, predict changes that the rock could undergo next if left in the natural setting. Answer the questions found on the page after the pictures. Figure 3. Photographs of a rock samples for classification, analysis, and prediction. Sample #1 Sample #2 Sample #3 Sample #4 Sample #5 Sample #6 Sample #7 Sample #9 Sample #8 Sample 1: Where would this rock fall on the rock cycle? In other words, is this an igneous, sedimentary, or metamorphic rock? What are possible changes that the rock could undergo next if left in the natural setting? Sample 2: Where would this rock fall on the rock cycle? In other words, is this an igneous, sedimentary, or metamorphic rock? What are possible changes that the rock could undergo next if left in the natural setting? Sample 3: Where would this rock fall on the rock cycle? In other words, is this an igneous, sedimentary, or metamorphic rock? What are possible changes that the rock could undergo next if left in the natural setting? Sample 4: Where would this rock fall on the rock cycle? In other words, is this an igneous, sedimentary, or metamorphic rock? What are possible changes that the rock could undergo next if left in the natural setting? Sample 5: Where would this rock fall on the rock cycle? In other words, is this an igneous, sedimentary, or metamorphic rock? What are possible changes that the rock could undergo next if left in the natural setting? Sample 6: Where would this rock fall on the rock cycle? In other words, is this an igneous, sedimentary, or metamorphic rock? What are possible changes that the rock could undergo next if left in the natural setting? Sample 7: Where would this rock fall on the rock cycle? In other words, is this an igneous, sedimentary, or metamorphic rock? What are possible changes that the rock could undergo next if left in the natural setting? Sample 8: Where would this rock fall on the rock cycle? In other words, is this an igneous, sedimentary, or metamorphic rock? What are possible changes that the rock could undergo next if left in the natural setting? Sample 9: Where would this rock fall on the rock cycle? In other words, is this an igneous, sedimentary, or metamorphic rock? What are possible changes that the rock could undergo next if left in the natural setting?
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Metamorphic Rocks
For this lab, you will be making observations and interpretations about metamorphic rocks. I
recommend that you print the data table provided and fill it in as you analyze each sample.
Then, use your table to answer the questions at the end of the lab. Also answer these questions on
our online class site so that you can get credit for the laboratory exercise.
Metamorphism
Metamorphic rocks form when pre-existing rocks are subjected to temperatures and/or pressures
that are different from the environment in which they form. For example metamorphism can be
caused by burial of rock, folding and thrusting of rock over other rock, heat from a pluton, or
pressure from subduction. During metamorphism, rocks may undergo mineralogical and textural
changes. During metamorphism, the rock does not melt. Instead it is a solid state
recrystallization.
Metamorphic Grade
Metamorphic grade is the intensity of metamorphism to which the rock was subjected. In other
words, it is a description of how much heat and pressure a rock has experienced in order to be
changed to its current metamorphic state. Metamorphic grade is described as being low grade,
medium grade, or high grade. During low-grade metamorphism, rock is exposed to relatively low
temperatures and pressures (300-400°C; less than 3-4 kilobars). During medium-grade
metamorphism, rock is exposed to intermediate temperatures and pressures (400-600°C; 4-12
kilobars). During high-grade metamorphism, rock is exposed to high temperatures and pressures
(600-800°C; 12-15 kilobars). It is by studying the mineralogy and textures of metamorphic rocks
that we are able to determine the degree or grade of metamorphism.
Mineralogical Changes
Each mineral is stable within a specific range of temperatures and pressures. When not at these
temperatures or pressures, minerals can become unstable and react with each other to form
new minerals. Therefore, we can analyze the suite of minerals in the rock and figure out what
temperatures and pressures would be possible for each of those minerals to be present in the
rock, thus determining the metamorphic grade.
Textural Changes
Textural refers to the size, shape, and orientation of grains in a rock. During metamorphism, heat
and pressure can change the textures of rocks. Consider the sizes of minerals. Minerals may
recrystallize to form larger crystals of the same minerals. For example, the calcite in
fossiliferous limestone will recrystallize into large, interlocking crystals of calcite, forming
marble, while the fossils, shells, and mud in the matrix are destroyed. Therefore, a rock with
larger crystals of calcite would be formed.
Some textural changes from metamorphism are a result of pressure being stronger in one
direction than another, resulting in deformation, or change in shape. During deformation, it is
common for platy minerals (like micas) to align perpendicular to the direction of compression,
creating what is called foliation. Foliation is a texture that results from the parallelism of platy
and flattened minerals in a metamorphic rock. Foliated rocks often have flat surfaces, especially

in the minerals are too small to be visible. If foliation is present, you know you are dealing with
low to medium metamorphism, where pressure was influential. Mica minerals do not withstand
high temperatures. At high temperatures, micas will react with minerals around them to form
feldspars and other minerals. If a metamorphic rock has bands of dark and light layers, it is
considered compositionally layered, and is a sign of high grade metamorphism. If a metamorphic
rock does not have layering or foliation, and instead has random, intergrown crystals, it is
referred to as nonfoliated. This is usually a sign that pressure was not involved in the
metamorphism.
Protolith
The protolith (proto=early, lith=rock), is the type of rock it used to be before the heat and
pressure were added, transforming the rock into the metamorphic rock it is now. This is also
often referred to as the parent rock. Since metamorphism can happen to any rock, even a
metamorphic rock can be a protolith for another metamorphic rock. However, for the purposes of
this class, we will go back all the way until the protolith was either a sedimentary or igneous
rock. For example, when shale (a fissile, sedimentary mudstone) is metamorphosed, it first
becomes slate, but upon application of more heat and pressure, the slate will change to phyllite,
then schist, and finally gneiss. Therefore, the protolith for slate, phyllite, schist, and gneiss is
shale. Gneiss actually has two protoliths, as seen in figure 1 below. This figure also shows the
protoliths and other characteristics of common metamorphic rocks, which you will use to analyze
metamorphic rocks.
Figure 1. Common Metamorphic Rocks
Major
Additional
Texture
Minerals/Material
Observations
Micas – muscovite, Dull appearance, similar
Foliated
biotite, etc.
to that of a chalkboard
Has a sheen to it;
Micas – muscovite,
Foliated
sometimes has wavy,
biotite, etc.
wrinkled surfaces
Micas – muscovite,
Foliated
Often glittery appearance
biotite, etc.
Feldspars, quartz,
Minerals are separated
Layered
hornblende
into light and dark layers
Nonfoliated

Calcite

Fizzes in acid

Nonfoliated

Quartz

Nonfoliated

Plant material (no
minerals)

Sometimes has a sugary
texture; sometimes shows
conchoidal fracture
Black, low density, semimetallic l...


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